Hard disk drives are common information storage devices essentially consisting of a series of rotatable disks that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body experiences a fluid air flow that provides sufficient lift force to “fly” the slider and transducer above the disk data tracks. The high speed rotation of a magnetic disk generates a stream of air flow or wind along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider body which enables the slider to fly above the spinning disk. In effect, the suspended slider is physically separated from the disk surface through this self-actuating air bearing. The ABS of a slider is generally configured on the slider surface facing the rotating disk, and greatly influences its ability to fly over the disk under various conditions.
As shown in FIG. 1 an ABS design known for a common catamaran slider 5 may be formed with a pair of parallel rails 2 and 4 that extend along the outer edges of the slider surface facing the disk. Other ABS configurations including three or more additional rails, with various surface areas and geometries, have also been developed. The two rails 2 and 4 typically run along at least a portion of the slider body length from the leading edge 6 to the trailing edge 8. The leading edge 6 is defined as the edge of the slider that the rotating disk passes before running the length of the slider 5 towards a trailing edge 8. As shown, the leading edge 6 may be tapered despite the large undesirable tolerance typically associated with this machining process. The transducer or magnetic element 7 is typically mounted at some location along the trailing edge 8 of the slider as shown in FIG. 1. The rails 2 and 4 form an air bearing surface on which the slider flies, and provide the necessary lift upon contact with the air flow created by the spinning disk. As the disk rotates, the generated wind or air flow runs along underneath, and in between, the catamaran slider rails 2 and 4. As the air flow passes beneath the rails 2 and 4, the air pressure between the rails and the disk increases thereby providing positive pressurization and lift. Catamaran sliders generally create a sufficient amount of lift, or positive load force, to cause the slider to fly at appropriate heights above the rotating disk. In the absence of the rails 2 and 4, the large surface area of the slider body 5 would produce an excessively large air bearing surface area. In general, as the air bearing surface area increases, the amount of lift created is also increased. Without rails, the slider would therefore fly too far from the rotating disk thereby foregoing all of the described benefits of having a low flying height.
As illustrated in FIG. 2, a head gimbal assembly 40 often provides the slider with multiple degrees of freedom such as vertical spacing, or pitch angle and roll angle which describe the flying height of the slider. As shown in FIG. 2, a suspension 74 holds the HGA 40 over the moving disk 76 (having edge 70) and moving in the direction indicated by arrow 80. In operation of the disk drive shown in FIG. 2, an actuator 72 moves the HGA over various diameters of the disk 76 (e.g., inner diameter (ID), middle diameter (MD) and outer diameter (OD)) over arc 75.
A preamplifier is typically connected to the head to supply write currents to the write head and receive currents from the read head. The suspension provides two functions: mechanical support and electrical connection between the head and the preamplifier. Rather than using physical wires to connect the head to the preamplifier, metal traces on the suspension are quite often used.
In the art, there are typically two types of wireless suspensions. In the first type, such as trace suspension assemblies (TSAs) and circuit integrated suspension (CISs), traces are built though a subtractive process (e.g., an etching operation) or through an additive process (e.g., a plating or deposition process) on the stainless steel flexure, with an insulative layer between the trace and the flexure. After the traces are set in place, the flexure can then be welded to other parts of the suspension. In the second type, such as flex suspension assemblies (FSAs) and flex on suspension (FOS), the traces are built on an insulation layer and then covered with another insulation layer to form a flex circuit. This circuit is then attached to the suspension with adhesive. Alternatively, an additional metal layer called a ground plane can be attached to the flex circuit before it is adhered to the suspension.
Typically four traces are supplied for a single head: one pair for the connection between the read head and the pre amplifier and one pair for the connection between the write head and the preamplifier. In the art, it is known that the stainless steel flexure, the suspension, and the ground plane (if one is provided) may provide some protection against electromagnetic interference (EMI). If this protection is not sufficient, then EMI can cause errors to occur in the data stream. Thus, there is a need for an improved system for controlling EMI in a suspension assembly.